The development of engines over the past few years have included increasing the horse power without increasing the displacement of the engine. To obtain the increased horsepower, it has been necessary to increase the combustion pressures within the combustion chamber which are transferred through the piston into the connecting rod and crankshaft.
Such increase in pressures have required the improvement of the integrity of the piston to withstand the increased stresses thereon. In the past and in many cases today, such pistons are made of aluminum or cast iron. Or, in some applications have used an articulated piston having a steel head and an aluminum skirt. Such an example is shown in U.S. Pat. No. 5,040,454 issued on Aug. 20, 1991 to Benny Ballheimer and Stephen G. Shoop.
As the pressures of engine designs increase, further requirements for the improvement of the integrity of the piston to withstand the increasing stresses thereon has become more apparent. As the pressures increase and consequently the stresses increase attempts have been made to resist, for example, bending stresses. One such example, is shown in U.S. Pat. No. 3,877,351 issued Apr. 15, 1975 to Eugen Barfiss. A ring zone of an upper part being made of steel and being supported by a lower part consisting of an aluminum alloy. The upper part and the lower part are joined by a bolted connection in a removable method of attachment. Additionally, U.S. Pat. No. 4,346,646 issued Aug. 31, 1982 to Jurgen Ellermann discloses a crown of steel being connected with a piston body of aluminum. An annular skirt supports the piston body. The crown and the piston body are joined by a bolted connection in a removable method of attachment.
Other piston assemblies are joined in a fixed manner such as by welding. For example, U.S. Pat. No. 5,359,922 issued Nov. 1, 1994 to Jose M. Martins Leites et. al. discloses a method of manufacturing an articulated piston head wherein two portions are joined by friction welding. U.S. Pat. No. 5,245,752 issued Sep. 21, 1993 to Andre Lippai et. al. discloses a two-piece piston having two portions friction welded together, U.S. Pat. No. 4,286,505 issued Sep. 1, 1981 to John K. Amdall discloses a two piece piston being joined by a brazing process, and U.S. Pat. No. 3,974,381 issued Aug. 10, 1976 to Manfred Rohrle, et. al. discloses a method of welding a workpiece including electron beam welding.
However, in many applications, the complexity of the piston design increases the cost of manufacturing. For example, with some welded designs flash occurs which can separate and contaminate the lubricating and cooling liquid and in other welded designs the position of the weld joint is difficult or nearly impossible to attain. And, with some bolted joints, additional strength is required at the bolted joint requiring additional parts and assembly time.
The present invention is directed to overcoming one or more of the problems as set forth above.